1 /* xalloc-oversized.h -- memory allocation size checking
2
3 Copyright (C) 1990-2000, 2003-2004, 2006-2023 Free Software
4 Foundation, Inc.
5
6 This file is free software: you can redistribute it and/or modify
7 it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
10
11 This file is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public License
17 along with this program. If not, see <https://www.gnu.org/licenses/>. */
18
19 #ifndef XALLOC_OVERSIZED_H_
20 #define XALLOC_OVERSIZED_H_
21
22 #include <stddef.h>
23 #include <stdint.h>
24
25 /* True if N * S does not fit into both ptrdiff_t and size_t.
26 N and S should be nonnegative and free of side effects.
27 This expands to a constant expression if N and S are both constants.
28 By gnulib convention, SIZE_MAX represents overflow in size_t
29 calculations, so the conservative size_t-based dividend to use here
30 is SIZE_MAX - 1. */
31 #define __xalloc_oversized(n, s) \
32 ((s) != 0 \
33 && ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) \
34 < (n)))
35
36 /* Return 1 if and only if an array of N objects, each of size S,
37 cannot exist reliably because its total size in bytes would exceed
38 MIN (PTRDIFF_MAX, SIZE_MAX - 1).
39
40 N and S should be nonnegative and free of side effects.
41
42 Warning: (xalloc_oversized (N, S) ? NULL : malloc (N * S)) can
43 misbehave if N and S are both narrower than ptrdiff_t and size_t,
44 and can be rewritten as (xalloc_oversized (N, S) ? NULL
45 : malloc (N * (size_t) S)).
46
47 This is a macro, not a function, so that it works even if an
48 argument exceeds MAX (PTRDIFF_MAX, SIZE_MAX). */
49 #if 7 <= __GNUC__ && !defined __clang__ && PTRDIFF_MAX < SIZE_MAX
50 # define xalloc_oversized(n, s) \
51 __builtin_mul_overflow_p (n, s, (ptrdiff_t) 1)
52 #elif (5 <= __GNUC__ && !defined __ICC && !__STRICT_ANSI__ \
53 && PTRDIFF_MAX < SIZE_MAX)
54 # define xalloc_oversized(n, s) \
55 (__builtin_constant_p (n) && __builtin_constant_p (s) \
56 ? __xalloc_oversized (n, s) \
57 : ({ ptrdiff_t __xalloc_count; \
58 __builtin_mul_overflow (n, s, &__xalloc_count); }))
59
60 /* Other compilers use integer division; this may be slower but is
61 more portable. */
62 #else
63 # define xalloc_oversized(n, s) __xalloc_oversized (n, s)
64 #endif
65
66 #endif /* !XALLOC_OVERSIZED_H_ */